Catalytic oxidative dehydrogenation of alkenes or alkadienes to furan compounds

ABSTRACT

Alkenes and/or alkadienes are contacted with molecular oxygen and an oxidative dehydrogenation catalyst consisting essentially of molybdenum, vanadium, oxygen, and at least one promoter selected from the group consisting of iron, cobalt, and nickel, to produce furan compounds.

United States Patent 1191 Farha, Jr, et a1,

1451 July 8,1975

[ CATALYTIC OXIDATIVE DEHYDROGENATION OF ALKENES 0R ALKADIENES TO FURAN COMPOUNDS [75] lnventors: Floyd E. Farha, Jr.; Marvin M.

Johnson; Donald C. Tablelr, all of Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

22 Filed: July 19, 1973 211 Appl. No.: 380,723

[52] 11.8. Cl. 260/346.1 R; 260/680 E; 252/470 [51] Int. Cl C07cl 5/14 [58] Fieltl of Search 260/3461 R, 680 E [56] References Cited OTHER PUBLICATIONS Ai, logyo Kagaku Zasshi 1971, 74(2), p. 1836, Chemical Abstracts 1971, Vol. 74, 125302.

Primary Examiner-Henry R. Jiles Assistant ExaminerBernard Dentz 16 Claims, N0 Drawings CATALYTMI OXllDATf /E DlElI-EYDRQGTENATHGN ()1 ALKENIES OR ALKADHENES TO) FURAN CQMTPQ UNDS This invention relates to oxidative dehydrogenation catalysts and the use thereof for the conversion of alkenes and/or alkadienes to furan compounds.

Furan compounds can react readily with oxygen under oxidation conditions to produce ring cleavage and the formation of polymers. Accordingly, the production of furan compounds by the oxidative dehydrogenation of hydrocarbons has generally been avoided. Recently it has been discovered that furan compounds can be produced by the oxidative dehydrogenation of hydrocarbons in the presence of certain specific catalysts without substantial conversion of the furan compounds to undesirable products. The search for additional catalysts suitable for this reaction continues.

Accordingly, it is an object of the present invention to provide a new and improved oxidative dehydrogenation catalyst. Another object of the invention is to provide a new and improved process for the conversion of alkenes or alkadienes to furan compounds. Other objects, aspects and advantages of the invention will be apparent from a study of the specification and the appended claims to the invention.

in accordance with the present invention there is provided an improved catalyst for the production of furan type compounds from alkenes and alkadienes having from 4 to 10 carbon atoms, which catalyst consists essentially of molybdenum, vanadium, oxygen and at least one promoter selected from the group consisting of iron, cobalt, and nickel.

If desired, these catalysts can be supported on conventional solid catalytic support materials, for example zinc oxide, silica, alumina, boria, magnesia, titania, zirconia, and mixtures thereof Where a catalyst support is employed, the support will generally constitute from about 10 to about 98, preferably from about 75 to about 95, weight percent of the total catalyst composition. Supports having surface areas in the range of about 2 to about 50 m /g, preferably in the range of about to about 20 m /g, are desirable. The atom ratio of molybdenum to vanadium will generally be in the range of about :1 to about 05:1, and preferably will be in the range of about 5:1 to about 1:1. The atom ratio of promoter to vanadium will generally be in the range of about 2:1 to about 0.1:1, and preferably will be in the range of about 1:1 to about 03:1.

The catalysts of the present invention can be prepared by many suitable techniques, for example coprecipitation, impregnation, ion exchange aqueous or nonaqueous solution or suspension mixing, or dry mixing. In general, any method can be employed which will provide a composition containing the desired elements in the defined proportions, and which has a catalytic surface area of at least about 0.05 to about m /g and preferably about 0.1 to about 5 m /g. Thus the catalyst components and/or compounds thereof can be combined in any suitable manner. Any compound of vanadium, molybdenum, or the promoter can be employed in the preparation of the catalyst so long as none of the compounds are detrimental to the final oxidative dehydrogenation catalyst and essentially all of the elements in the compounds employed, other than the vanadium, molybdenum, promoter metal and oxygen, are removed from the final catalyst by washing or by volatilization. However, small or trace amounts of some other elements which can be involved in the preparation of the catalyst can be tolerated in the final catalytic composition. For example, if alkali metal or alkaline earth metal hydroxides are employed in the preparation of the catalyst, very small residual amounts of such alkali metal and alkaline earth metals are not detrimental. Similarly, if nickel sulfate, cobalt sulfate or iron sulfate is employed in the preparation of the catalyst, small residual amounts of sulfur can be tolerated.

Generally, however, the preferred vanadium, iron, cobalt, nickel and molybdenum compounds are the oxides of these elements or compounds which are converted to the oxide on calcination. Thus, suitable com pounds include the oxides, nitrates, halides, sulfates, oxalates, acetates, carbonates, propionates, tartrates, hydroxides, ammonium salts and the like, and mixtures thereof. Examples of these compounds include cobalt nitrate, cobalt acetate, cobalt hydroxide, cobalt oxide, cobalt propionate, iron oxide, iron nitrate, molybdenum oxide, ammonium molybdate, nickel oxide, nickel chloride, nickel nitrate, nickel carbonate, vanadium oxide, vanadium sulfate, ammonium vanadate, and the like, and mixtures thereof.

One technique for forming an unsupported catalyst of the present invention comprises mixing one or more molybdenum compounds, one or more vanadium compounds, and one or more promoter metal compounds.

The compounds can be admixed in the form of dry compounds and then calcined, or the compounds can be admixed in the presence of a diluent to form a paste, which may be dried, if desired, before calcining. A particle forming step such as pelletizing or screening can precede the drying step or the calcining step.

A technique for forming a supported catalyst of the present invention comprises sequentially impregnating the support with solutions or dispersions of each component compound, drying and calcining the impregnated support.

The calcining step will be accomplished under conditions which ensure the conversion of any nonoxide compounds to the oxide form and the volatilizing of any undesired elements. In general the calcining step comprises heating the catalyst composition to a temperature in the range of about 800 F to about 1500 F for a time in the range of about 1 to about 40 hours. Presently preferred calcining conditions comprise a temperature in the range of about 850 F to about l400 F for a time in the range of about 2 to about 24 hours in the presence of a molecular oxygen containing gas, for example, air.

Suitable feeds for conversion to furan compounds include the unsaturated acyclic hydrocarbons, particularly the acyclic alkenes and acyclic alkadienes having from 4 to 10 carbon atoms. Examples include nbutenel, butene-Z, n-pentene-l, isopentene, hexenel, heptene-Z, octene-l, decene-l, Z-methylbutene-l, hexene-3, Z-ethylbutene-l, 2-methylpentene-3, 3 ethylhexene-Z, butadiene-l,3, pentadiene-l,3, isoprene, hexadiene-l,3, decadiene-l,3, and the like, and mixtures thereof. Acyclic alkadienes having from 4 to 5 carbon atoms are presently preferred.

The furan compounds produced by the process of the present invention have the formula wherein each R is individually selected from the group consisting of hydrogen and alkyl radicals having from 1 to 6 carbon atoms, the total carbon atoms in the R radicals being in the range of O to 6. Representative furan compounds. However, the reaction effluent can also contain unreacted feed material, alkenes including ethylene, propylene and butenes, water, oxides of carbon, alkenylcycloolefins, crotonaldehyde, acetaldeproducts include furan, 2-methylfuran, 3-methylfuran, hyde and other oxygenated products. The furan com- 2,5'-diethylfuran, 2-n-hexylfuran, I 2-isopropyl-3- pounds can be recovered by suitable techniques, for exmethylfuran, 3-n-pi-opylfui-a 3-mcthyl-4 b t lf ampleby condensation from the reactor gas effluent and the like. followed by distillation. Unconverted alkenes and/or In accordance with the present invention a h d alkadienes can be recovered and recycled to the reacbon feed comprising one or more acyclic lk n a dtor, as can other materlals such as crotonaldehyde /or one or more acyclic alkadienes is contacted, under Whlcl} are collvfirtlble to i COmPQUTIdS finder the suitable reaction conditions for conversion to furan T630110" C0nd1t10fl$- If slred, the conversion of a1- compounds, with a molecular oxygen containing gas in kelfes to furall comPounds can be conqucted m two the presence of the hereinabove d fi d catalyst The action zones 1n series. The first reaction zone can be molecular Oxygen containing gas can be high purity operated under conditions favorable for the conversion ygeh; oxygen diluted with an inert diluent Such as him} of the alkenes to alkadienes, while the second reaction gen flue gas containing residual oxygen, air o any zone can be operated under conditions favorable to the Other Source of molecular oxygen which is at least conversion of the alkadienes to furan compounds. The sentially free of contaminants which would be detrieffluent m the first 9 Z9116 can be sublected mental to the desired reaction. In a presently preferred to convenuonal Separanon techmques to embodiment the oxidative dehydrogenation process is converted alkenes for recycle to the first reactlon zone Carried out in the absence of any halogen In general and a concentrated alkadiene stream for feed to the the temperature will be in the range of about 5000 R second reaction zone. If desired, the total effluent from to about 12000 F. and preferably will he in the range the first reaction zone can be passed directly to second of about 7000 F to about 1 6 R Any Suitable pressure reaction zone without separation step. The effluent of can be e m pl 0y e d, but in general the pressure will he in the second reaction zone can be processed for recovery the range of about 005 to about 250 psia and prefera and recycle of unreacted alkadienes to the second reacbly will be in the range of about 0.1 to about 25 psig. zone and for recovel'y of a @mpound P The hydrocarbon feed rate will generally be in the catalyst of present Invention can be range of about 10 to about 1000 standard cubic feet of ployed m f reactlon zones or anothef Sultable alkenes and/or alkadienes per hour per cubic foot of hyimgenatm Fatalyst can be employs? catalyst bed (GHSVL and preferably will be in the action zone while the present catalyst ls utilized in the range of about 100 to about 500 Gl-lSV. The mol ratio Second reaction Zone of molecular oxygen to alkenes and alkadienes will genh followmg example 15 presented m further erahy be in the range of about 01:1 to about and tratlon of the invention and should not be construed 1n preferably will be in the range of about 0.5:1 to about undue hmltanon thereof 2:1. Steam can be employed in the reaction zone as a diluent and heat transfer agent. When steam is utilized, EXAMPLE the mol ratlo of steam to alkenes and alkadienes W111 generally be in the range of about 0.1 :1 to about :1, each of a Saws of runs employing Various cataand preferably will be in the range of about 5:1 to Y butadlefle GHSV) Was contacted with 1110- about 30:1. lecular oxygen (400 GHSV) and steam (8000 GHSV) The alkenes, if present, are largely converted'to the in the presence of about 2 cc of the respective catalyst. corresponding alkadienes. The alkadienes, in turn, are The reaction conditions and results are Shown in the converted in significant quantities to the corresponding following table:

TABLE Atom Ratios Conversion Selectivity to Molybde- Promoter of Furan Selectivity Acetaldehyde Furan and num to to Temp. Butadiene Yield 'to Furan Yield Acetaldehyde Runs Vanadium Vana- Promoter F dium 1 2/1 0.47/1 Cobalt 700 3.3 1.6 48.5 NW" 48.5 2 2/1 0.47/1 Cobalt 800 16.5 9.1 55.0 NT 55.0 3 2/1 0.47/1 Cobalt 900 22.5 9.5 48.2 NT 48.2 4 2/1 0.47/1 Cobalt 1000 23.6 8.2 34.8 NT 34.8 5 2/1 0.47/1 Cobalt 800 8.5 6.4 75.4 NT 75.4 6 2/1 0.47/1 Cobalt 900 17.8 10.5 59.0 NT 59.0 7 2/1 0.47/1 Cobalt 1000 22.3 8.8 39.4 NT 39.4 8 4/1 0.94/1 Cobalt 800 6.2 4.4 71.0 NT 71.0 9 4/1 0.94/1 Cobalt 900 17.8 10.5 59.0 NT 59.0 10 4/1 0.94/1 Cobalt 1000 23.0 10.4 45.1 NT 45.1 1 1 4/1 0.47/1 Cobalt 700 3.6 1.4 38.8 0 38.8 12 4/1 0.47/1 Cobalt 800 19.4 8.9 45.8 0 47.7 13 4/1 0.47/1 Cobalt 900 21.2 9.2 43.4 0.7 46.7 14 4/1 0.47/1 Cobalt 1000 20.8 8.6 41.3 1.0 46.4 15 4.2/1 0.47/1 Cobalt 1000 21.5 8.3 38.6 1.1 43.5 16 4.1/1 0.49/1 Cobalt 1000 22.3 9.4 42.1 1.2 47.5 17 2/1 0.47/1 Cobalt 800 4.8 3.7 75.6 0 75.6 18 2/1 0.47/1 Cobalt 900 14.3 10.2 71.3 v 0.5 74.9 19 2/1 0.47/1 Cobalt 1000 19.2 9.5 49.4 0.7 54.4

TABLE -Contmued Atom Ratios Conversion Selectivity to Molybde- Promoter of Furan Selectivity Acetaldehyde Furan and num to to Temp. Butadiene Yield to Furan Yield Acetaldehyde Runs Vanadium Vana- Promoter F dium 20 2/1 0.46/1 lron 800 11.2 7.4 66.0 0.3 69.1

21 2/1 0.46/1 lron 900 26.0 11.8 45.4 1.2 49.9

22 2/1 0.46/1 lron 1000 20.6 8.3 40.5 0.7 43.8

23 4/1 0.92/1 lron 1000 21.8 8.3 38.1 1.0 42.5

24 4/1 0.46/1 Iron 800 18.7 11.3 60.3 0.6 63.5

25 4/1 0.46/1 lron 900 20.8 10.6 50.9 0.8 54.7

26 4/1 0.46/1 lron 1000 20.7 8.2 39.6 0.8 43.8

27 4/1 0.94/1 Cobalt 900 30.6 11.6 37.9 0.3 38.8

28 4/1 0.46/1 lron 900 32.6 11.6 35.6 0.3 37.0

29 4/1 0.40/1 Nickel 900 31.2 11.7 37.5 0.4 38.7

30 2/1 0.4/1 Cobalt 1000 27.2 2.6 9.5 NT 9.5

31 2/1 l/l Cobalt 800 8.5 2.2 25.9 NT 25.9

32 NA" NA None (B) O 0 0 0 33 NA NA Cobalt 800 4.5 2.7 60.0 0 60.0

34 NA NA Cobalt 900 3.9 2.4 61.5 0 61.5

35 2/1 NA None 800 12.9 9.3 72.1 0 72.1

36 2/1 NA None 900 11.6 8.6 74.1 0.3 76.7

37 2/1 NA None 1000 20.1 8.0 39.8 0.8 43.7

38 NA NA Cobalt 1000 1.2 0.5 41.7 0 41.7

39 4/1 NA None 800 5.5 4.0 72.7 0 72.7

40 4/l NA None 900 7.5 5.9 78.6 0 78.6

41 4/1 NA None 1000 20.0 10.8 54.0 0.6 57.0

""NA means not applicable "NQ activity at 700-1000? "Not tested The catalysts were generally prepared in small lots of about 20 grams or less using an amount of each component required to give the atom ratios shown in the table.

The catalysts of runs l-l4, 17-19 were made by mixing together an aqueous solution or dispersion consisting of ammonium molybdate, ammonium vanadate, cobalt acetate and water, evaporating the mixture to dryness and calcining the product. The catalyst of runs l-l4 was calcined at 900 F for 16 hours. The catalysts of runs -15 and 17-19 were calcined at 1000 F for 2 hours.

The catalyst of run was made by dry mixing together ammonium molybdate, ammonium vanadate and cobalt acetate, pelleting the mixture and calcining the pellets at 1000 F for 5 hours. The catalyst of run 16 was made by mixing together vanadium trioxide, molybdenum trioxide and tricobalt tetroxide (i.e., C0 0 pelleting the mixture and calcining the pellets at 1000 F for 5 hours.

The catalysts of runs -26 were made by mixing together an aqueous solution or dispersion consisting of ammonium molybdate, ammonium vanadate, ferric nitrate and water, evaporating the mixtures to dryness and calcining the products at 1000 F. for 2 hours.

The catalysts of runs 27-29 were made by mixing together an aqueous solution or dispersion consisting of water, ammonium molybdate, ammonium vanadate, and one of cobalt acetate (for run 27), ferric nitrate (for run 28) and nickel acetate (for run 29). To the mixtures was added sufficient ammonium hydroxide to give an alkaline reaction after which the mixtures were evaporated to dryness and the products calcined at 1000 F for 2 hours.

The catalysts of runs and 31 are supported catalysts, the support being ZnO in each instance. The catalyst/support weight ratio was 1235/8115 in run 30 and 203/797 in run 31. The catalyst composition of run 30 was made by impregnating the support with aqueous solutions of ammonium molybdate, ammonium vanadate and cobaltous nitrate and evaporating to dryness. The catalyst composition of run 31 was made in a similar fashion except that the cobalt salt used was cobaltous acetate. The dried composites were calcined at 900 F for 16 hours.

The catalysts of runs 32-41 were controls. All of them were calcined at 1000 F for 2 hours after preparation. The catalyst of run 32 was made by evaporating an aqueous solution of ammonium molybdate to dryness. The catalyst of runs 33 and 34 was made by mixing together aqueous solutions of ammonium molybdate and cobaltous acetate and evaporating the mixture to dryness. The catalyst of runs 35-37 was made by mixing together a heated solution or dispersion consisting of ammonium molybdate, ammonium vanadate and water and evaporating the mixture to dryness. The catalyst of run 38 was made in a similar fashion to the catalyst of runs 33 and 34 except /2 the quantity of the cobalt salt was used. The catalyst of runs 39-41 was made in a similar fashion to the catalyst of runs 35-37 except /2 the quantity of ammonium vanadate was used.

The catalysts were normally tested at reactor temperatures of 700, 800, 900 and 1000 F in sequence. Data are reported only for those runs in which significant amounts of furan were produced.

The gaseous effluents, on a dry basis, were analyzed by means of gas-liquid chromatography. Products found included unreacted butadiene, furan, acetaldehyde, carbon oxides, ethylene, propylene and butenes. The reported selectivities to furan and furan plus acetaldehyde are modified selectivities based on the above gaseous product analyses. The yields of furan and acetaldehyde are expressed in terms of moles per moles of butadiene feedstock.

Inspection of the Table reveals that molybdenum trioxide (run 32) and a binary mixture of molybdenum trioxide and cobalt oxide (runs 33, 34 and 38) at lVlo/Co ratios of l/ 11 and 2/11 are ineffective in converting butadiene into furan. However, catalysts containing molybdenum and vanadium in atom ratios of 2/11 and 4/11 (runs 35-37 and 39-41) are effective at reactor temperature of 800 to 1000 F in converting butadiene to furan. Based on selectivity, the best temperature in these runs was 900 F. The best conversion of feedstock occurred at 1000 F with considerable loss in selectivity.

The addition of an iron metal promoter to the molybdenum/vanadium combination appears to activate the catalyst so that a larger conversion of butadiene occurs at a lower temperature (800, 900). Compare runs 36 and 40 with runs 3, 6, 9, 13, 21, 25, 27-29. With the unpromoted Mo/V catalyst the best Mo/V atom ratio occurs at 2/1 for reactor temperature of 900 or 800 F. When an iron metal promoter is added to the Mo/V combination the atom ratio of Mo/V of 4/1 appears to generally be more desirable based on conversion and furan yields. The primary effect of the promoter metals is to activate the basic Mo/V combination at the lower temperatures. 1

Reasonable variations and modifications are possible within the scope of the foregoing disclosure and the appended claims to the invention.

What is claimed is:

1. A process which comprises reacting at least one unsaturated acyclic feed hydrocarbon selected from the group consisting of alkenes and alkadienes having from 4 to 10 carbon atoms, with oxygen in contact with a catalyst consisting essentially of molybdenum, vanadium, oxygen, and at least one promoter selected from the group consisting of iron, cobalt, and nickel, under suitable vapor phase reaction conditions to convert said at least one unsaturated feed hydrocarbon to at least one furan compound having. the formula wherein each R is individually selectedfrom the group consisting of hydrogen and alkyl radicals having from 1 to 6 carbon atoms, the total carbon atoms in the R radicals being in the range of to. 6; and recovering at least a portion of the furan compounds thus produced.

2. A process in accordance-with-claim 1 wherein said reaction conditionsgcomprisega temperature in the range of. about 500 F to-about' l200-F, an unsaturated acyclic hydrocarbon feedrate in the range of about 10 to about 1000 GHSV, and an oxygen-to-feed unsaturated acyclic hydrocarbon mol ratio in the range of about 0.1:1 to about 3:1. I

3. A-process in accordance with claim 1 wherein the atom ratio of molybdenum ,to vanadium is in the range of about 10:1 to about 0.5:1, and the atom ratio of promoter to vanadium, is in the range of about 2:1 to about i 4. A process in accordance with claim 1 whereinthe atom ratio of molybdenum to vanadium is in the range of about 5:1 to about l:1, and the atom .ratio of promoter to vanadium is in the range of about 1:1 to about 0.3:1. i

5. A process in accordance with claim 4 wherein said feed hydrocarbon comprises at least one acyclic alkadiene having from 4 to 5 carbon atoms.

6. A process in accordance with claim 5 wherein said feedhydrocarbon comprises butadiene.

7. A process in accordance with claim 6 wherein said promoter is cobalt.

8. A process in accordance with claim 6 wherein said promoter is iron.

9. A process in accordance with claim 6 wherein said promoter is nickel. i

10. A process which comprises reacting under suitable reaction conditions at least one unsaturated acyclic feed hydrocarbon selected from the group consisting of alkenes and alkadienes having from 4 to 10 carbon atoms,with oxygen in contact with a catalyst consisting essentially of molybdenum, vanadium, oxygen, and at least one promoter selected from the group consisting of iron, cobalt, and nickel, to produce at least one furan compound having the formula wherein each R is individually selected from the group consisting of hydrogen and alkyl radicals having from 1 to 6 carbon atoms, the total carbon atoms in the R radicals being in the range of O to 6; said reaction conditions comprising atemperature in the range of about 500F to about 1200F; and recovering at least a portion of the furan compounds thus produced.

11. A process in accordance with claim 10 wherein the atom ratio of molybdenum to vanadium is in the range of about 5:1 to about. 1:1, and the atom ratio of promoter to vanadium is in the range of about 1:1 to about 0.3: 1; and wherein said reaction conditions comprise a .temperaturein the range of about 700F to about 1100F, a pressure in the rangeof about 0.1 to about 25 psig, an unsaturated acyclic hydrocarbon feed rate in the range of about to about 500 GHSV, and an oxygen-toafeed unsaturated acyclic hydrocarbon mol ratio in the range of about 0.5:] to about 2:1.

12. A process in accordance with claim 11 wherein said feed hydrocarbon comprises at least one acyclic alkadiene having from. 4 to 5 carbon atoms.

13. A process in accordance with claim 12 wherein said feed hydrocarbon comprises butadiene.

14. A process in accordance with claim 13 wherein said promoter is cobalt.

' 15. A process in accordance with claim 13 wherein said promoter is iron.

16. A process in accordance with claim 13 wherein said promoter is nickel. 

1. A process which comprises reacting at least one unsaturated acyclic feed hydrocarbon selected from the group consisting of alkenes and alkadienes having from 4 to 10 carbon atoms, with oxygen in contact with a catalyst consisting essentially of molybdenum, vanadium, oxygen, and at least one promoter selected from the group consisting of iron, cobalt, and nickel, under suitable vapor phase reaction conditions to convert said at least one unsaturated feed hydrocarbon to at least one furan compound having the formula
 2. A process in accordance with claim 1 wherein said reaction conditions comprise a temperature in the range of about 500* F to about 1200* F, an unsaturated acyclic hydrocarbon feed rate in the range of about 10 to about 1000 GHSV, and an oxygen-to-feed unsaturated acyclic hydrocarbon mol ratio in the range of about 0.1:1 to about 3:1.
 3. A process in accordance with claim 1 wherein the atom ratio of molybdenum to vanadium is in the range of about 10:1 to about 0.5:1, and the atom ratio of promoter to vanadium is in the range of about 2:1 to about 0.1:1.
 4. A process in accordance with claim 1 wherein the atom ratio of molybdenum to vanadium is in the range of about 5:1 to about 1:1, and the atom ratio of promoter to vanadium is in the range of about 1:1 to about 0.3:1.
 5. A process in accordance with claim 4 wherein said feed hydrocarbon comprises at least one acyclic alkadiene having from 4 to 5 carbon atoms.
 6. A process in accordance with claim 5 wherein said feed hydrocarbon comprises butadiene.
 7. A PROCESS IN ACCRODANCE WITH CALIM 6 WHEREIN SAID PROMOTER IS COBALT.
 8. A process in accordance with claim 6 wherein said promoter is iron.
 9. A process in accordance with claim 6 wherein said promoter is nickel.
 10. A process which comprises reacting under suitable reaction conditions at least one unsaturated acyclic feed hydrocarbon selected from the group consisting of alkenes and alkadienes having from 4 to 10 carbon atoms, with oxygen iN contact with a catalyst consisting essentially of molybdenum, vanadium, oxygen, and at least one promoter selected from the group consisting of iron, cobalt, and nickel, to produce at least one furan compound having the formula
 11. A process in accordance with claim 10 wherein the atom ratio of molybdenum to vanadium is in the range of about 5:1 to about 1:1, and the atom ratio of promoter to vanadium is in the range of about 1:1 to about 0.3:1; and wherein said reaction conditions comprise a temperature in the range of about 700*F to about 1100*F, a pressure in the range of about 0.1 to about 25 psig, an unsaturated acyclic hydrocarbon feed rate in the range of about 100 to about 500 GHSV, and an oxygen-to-feed unsaturated acyclic hydrocarbon mol ratio in the range of about 0.5:1 to about 2:1.
 12. A process in accordance with claim 11 wherein said feed hydrocarbon comprises at least one acyclic alkadiene having from 4 to 5 carbon atoms.
 13. A process in accordance with claim 12 wherein said feed hydrocarbon comprises butadiene.
 14. A process in accordance with claim 13 wherein said promoter is cobalt.
 15. A process in accordance with claim 13 wherein said promoter is iron.
 16. A process in accordance with claim 13 wherein said promoter is nickel. 